Characterization of the instrument temperature dependence of Brewer total ozone column measurements

The instrumental temperature correction to be applied to the ozone measurements by the Brewer spectrophotometers is derived from measurements of the irradiance from an internal halogen lamp in the instrument. These characterisations of the Brewer instruments can be carried out within a thermal chamber, varying the temperature from −5 °C to +45 °C, or during field measurements, making use of the natural change in ambient temperature. However, the internal light source used to determine the thermal sensitivity of the instrument could be affected in both methods by the temperature variations as well, which may affect the determination of the temperature coefficients. In order to validate the standard procedures for determining Brewer's temperature coefficients, two independent experiments using both external light sources and the internal lamps have been performed within the ATMOZ Project. The results clearly show that the traditional methodology based on the internal lamps is not affected by possible temperature effects on the internal lamps. The three methodologies yielded equivalents results, with differences in total ozone column below 0.08 % for a mean diurnal temperature variation of 10 °C.